overfeeding or effieciant nurser???

So over the past few weeks ive noticed that my LO will only nurse on one side for about 10min tops and wont take the toher boob....but when he gets a bottle at day care he takes about 5-6oz, he is content for around 3-4 hrs either way....but im thinking there is no way that he is getting 5-6 oz outta one boob in 10min.....right??? I know that he is more effiecent than the pump and when I pump i get 4-5oz outta both boobs,,,,so would you say ihe is overeating at the bottle or really good nurser. or does it not matter....if he is happy